SV40 is a small virus but in its approximately 5200 base pairs is enough information either to productively grow in a permissive cell, or to convert a normal cell into a transformed one. The conversion is usually genetically stable enough to generate clonable lines of transformed cells. Some of these lines lose so much of their normal growth control that they acquire the capacity to grow as tumors. Since the total DNA sequence of SV40 is known, it is somewhat surprising that the mechanism of action of SV40 in maintaining the various transformed state in vitro is not at all well understood. Also, and probably not coincidentally, precisely which SV40-encoded molecules are necessary for maintenance of any of these states is an unsettled issue as well. The first question cannot be easily asked without a study of the second. Yet, few single laboratories have the capacity to ask both in a careful way. We propose here to ask both, through an interacting set of six separate collaborative projects directed at the sequence-protein-function relationships of the SV40 transforming genes. We will initially test the hypothesis that variant non-lytic forms of large T are essential for full expression of the transformed phenotype. 1. Directed deletion of SV40 DNA and analysis of lytic function. 2. Mapping and recovering SV40 from within transformed cells. 3. Transfection/transformation with novel SV40 DNA sequences. 4. T antigen: properties and activities of variant lytic and transformed cells. 5. Directed methylation of SV40 DNA analysis of methylation. 6. SV40 RNA processing (oocyte).